The invention relates to a wing structure in an aircraft and a fastening element and a wing rib for fastening stringers to a wing frame of the aircraft.
FIG. 1 shows a typical structure of an aircraft wing in cross-section. The wing comprises an upper skin 1 forming the upper surface of the wing and a lower skin 2 forming the lower surface of the wing. A support structure of the wing is placed between the skin plates and comprises transverse wing ribs 3 in relation to the longitudinal direction E of the wing. The wing ribs are arranged at a predetermined distance from one another. The wing rib is typically made of a plate material and the crosscut thereof substantially resembles the letter C and comprises a vertical plate and horizontal plates in the upper and lower ends of the vertical plate. The forward edge of the wing also includes a front spar 4 and correspondingly the aft edge includes a rear spar 5. Several parallel stringers 6 fastened to the wing rib are placed longitudinally with the wing both on the upper surface and lower surface of the wing. In general, the crosscut of the stringer substantially resembles the letter L or T. The vertical portion of the stringer is arranged into recesses 3a formed on the upper and lower portions of the wing rib. The skins of the wing are further fastened to the horizontal outer surface of the stringers, as FIG. 2 shows. As heavy vertical loads are placed upon the wing rib the structure of the rib is generally stiffened by arranging vertical supports 7 at the side of the wing rib.
The wing frame is still at present made mainly of aluminium alloys applicable to aircraft manufacturing or of other light alloys. Furthermore, the different components of the wing frame are attached together using separate fastening portions made of metal. FIG. 3 shows an example of such a fastening portion 8. The fastening portions are riveted to the wing rib, and thereafter the stringer is riveted to the fastening portion. If the fastening portion is not for some reason exactly in the right place, a required number of shim plates is arranged between the fastening portion and the stringer in order to compensate for the dimensional deviations. As each joint typically comprises two or more fastening portions, whereof each one is separately riveted to the wing rib and correspondingly to the stringer, the assembly of the wing frame becomes laborious. The number of required components is also high, which naturally increases the weight of the structure. The manufacture of current wing structures is slow and expensive.
The aircraft industry aims to continuously develop lighter and at the same time more durable structures. Consequently, the composite structures are gradually replacing the use of aluminium and corresponding metals as the material for making wing frames. Tests have been carried out for making wing ribs of carbon fibre reinforced plastic. What has become a problem is that a dimensional accuracy equalling the one achieved when manufacturing conventionally using metal is not always achieved in composite production. The cure cycle of the composite cause deformations that are difficult to handle for the components to be made, whereas the metallic components can be machined in accurate dimensions. The dimensional deviations caused by the composite deformations lead to all kinds of problems when assembling the wing frames. The components must be fastened using fastening portions, which cannot be arranged in position owing to the dimensional deviation until the wing is in an assembling stage, thus making the assembly very difficult and slow.
It is an object of the present invention to provide a new and improved system for fastening stringers in a wing frame to a wing rib.
The invention relates to an aircraft wing structure comprising an upper skin forming the upper surface of the wing and a lower skin forming the lower surface of the wing, and a wing frame between said skins,
whereby the wing frame comprises at least one transverse wing rib and at least one longitudinal upper stringer, to which the upper skin is fastened and correspondingly at least one lower stringer, to which the lower skin is fastened, and also a front spar forming the forward edge of wing frame fastened to the wing rib and correspondingly a rear spar forming the aft edge of the wing frame,
wherein the wing rib is an elongated portion comprising a first vertical side surface and correspondingly a second vertical side surface, whereby at least one elongated fastening element extending from the upper part of the side surface to the lower part of the side surface is arranged to at least one side surface of the wing rib,
which fastening element comprises a substantially plate-like flexible portion, whose first longitudinal edge is fastened to be immovable to the side surface of the wing rib, and the second longitudinal edge of the flexible portion comprises a stiffening portion,
the flexible portion in the fastening element is formed to be bendable in the longitudinal direction of the wing rib, whereby the flexible portion enables to move the stiffening portion a predetermined distance in the longitudinal direction of the wing rib,
the first and second ends of the stiffening portion in the fastening element comprises fastening portions, from which the fastening element is fastened to the stringer on the upper surface side of the wing and correspondingly to the stringer on the lower surface side of the wing, and
which stiffening portion in the fastening element is arranged to carry vertical loads between said stringers.
The invention also relates to a fastening element intended to fasten the components in the aircraft wing frame together, and the wing frame comprising at least one transverse elongated wing rib and at least one longitudinal stringer above the wing rib and correspondingly at least one stringer beneath the wing rib, and
the fastening element being an elongated part which can be arranged onto the vertical side surface of the wing rib,
the fastening element comprising a substantially plate-like flexible portion with a first longitudinal edge and a second longitudinal edge, whereby the first longitudinal edge of the flexible portion can be arranged onto the vertical side surface of the wing rib,
the second longitudinal edge of the flexible portion in the fastening element comprises a stiffener, and a first fastening portion is formed at the first end of the stiffener and correspondingly a second fastening portion is formed at the second end of the stiffener for fastening the upper surface stringer and correspondingly the lower surface stringer of the wing,
the structure of the stiffener in the fastening element is stiff and capable of carrying vertical loads, and
the flexible portion in the fastening element is formed to be bendable in the transverse direction of the fastening element allowing the stiffening portion to be moved in the longitudinal direction of the wing rib by bending the flexible portion.
The invention further relates to a wing rib, which is a part of the aircraft wing frame, the wing rib being an elongated part made of fibre reinforced plastic intended to be arranged in the transverse direction of the wing and to which the longitudinal stringers on the upper and lower surface sides of the wing are intended to be fastened,
the wing rib comprises a first vertical side surface and a second vertical side surface, whereby at least one side surface of the wing rib comprises at least one elongated fastening element, which is transverse in relation to the longitudinal axis of the wing rib and protrudes from the side surface, for connecting the stringer on the upper surface of the wing and the stringer on the lower surface of the wing to the wing rib,
the fastening element comprises a stiffening portion, whose first end includes a first fastening portion and the second end a second fastening portion for fastening the stringers of the wing, and the stiffener in the fastening element is formed so as to carry the vertical loads between the stringers,
a substantially plate-like flexible portion formed to bend in the transverse direction of the fastening element is placed between the stiffening portion and the wing rib, thus allowing the stiffening portion to be moved in the longitudinal direction of the wing rib by bending the flexible portion,
the fastening element is made of fibre reinforced plastic and the fastening element is integrated into the structure of the wing rib so that at least a part of the reinforcing fibres and plastic matrix in the fastening element and the wing rib is common, the fastening element thus being a fixed structural part of the wing rib.
The essential idea of the invention is that one or more elongated fastening elements protruding from the side surface of the wing rib and extending from the upper part of the wing rib to the lower part of the wing rib are arranged to at least one side surface of the wing rib. Fastening portions are formed at the outer ends of the fastening elements for fastening the stringers of the wing, the fastening element thus functioning at the same time as the fastening element of the stringer on both the upper surface and the lower surface of the wing.
The fastening element comprises a substantially plate-like flexible portion, which is transverse in relation to the vertical side of the wing rib. The first longitudinal edge of the flexible portion is fastened to be immovable onto the side surface of the wing rib. The flexible portion is also dimensioned and shaped so that it may bend if necessary in relation to the planar surface thereof in the transverse direction, i.e. in the longitudinal direction of the wing rib. The second longitudinal edge of the flexible portion, in turn, comprises a stiffened portion that endures pressing and bending, thus allowing the stiffening portion to carry the loads in the vertical direction of the wing. Fastening portions are formed at both longitudinal ends of the stiffened portion for fastening the stringers of the wing.
The invention provides such an advantage that two stringers, one on the upper side of the wing and the other on the lower side of the wing, can be fastened using a single fastening element. The assembly of the wing frame is more rapid compared with prior art solutions, as the number of components to be joined and the number of joints to be performed is smaller. The structure is also less complicated and lighter. Furthermore, as the flexible portion in the fastening element compensates for the dimensional deviations possibly created during the manufacture and assembly of the components, the fastening elements can be fastened to the wing rib before the actual assembly. In such a case the assembly of the wing frame is easier and faster than before. Separate shim plates are no longer needed during assembly. Another factor that simplifies and lightens the structure is that vertical stiffeners need no longer be fastened to the wing ribs, as the stiffening portion in the fastening element carries vertical loads. The flexible portion fastened to the side of the wing rib stiffens the wing rib in the vertical direction.
The essential idea of a preferred embodiment is that the fastening portions formed at the stiffener ends are made to bend in the transversal direction of the fastening element. The fastening portions are both capable of bending separately, whereby the possible mutual deviation of the position of the stringers placed above and beneath the wing rib in the longitudinal direction of the wing rib can be compensated without a harmful torque being created to the fastening element structure.
The essential idea of a second preferred embodiment of the invention is that the stiffened portion is plate-like, and that is transversely arranged to the free longitudinal edge of the flexible portion. Then the crosscut of the fastening element substantially resembles the letter T or L. Such a fastening element is easy to manufacture and very light.
The essential idea of a third preferred embodiment of the invention is that the flexible portion comprises at least one cut-through opening. Such openings can in a simple way affect the stiffness of the flexible portion. The openings also reduce the weight of the structure. According to an application the flexible portion includes an elongated opening.
A fourth preferred embodiment of the invention provides the essential idea that the wing rib is made of fibre reinforced plastic, and that the fastening elements are integrated to the wing rib structure. The wing rib and the fastening elements form an integral unit, where the number of separate parts belonging to the wing structure is smaller and the number of joints to be made during assembly is reduced. Furthermore, the integral structure endures loads better and the structure thereof can be made lighter. According to an implementation the fastening element is a preproduced part, what is known as an insert, which can be arranged to the structure of the side surface of the wing rib when manufacturing the wing rib. The insert can, for example, be laminated or glued to the side of the wing rib. Still according to an implementation the fastening element is also made of fibre reinforced plastic and it is formed in the same mould and during the same manufacturing stage as the rest of the wing rib structure. Then the wing rib and the fastening elements are at least partly composed of common reinforcing fibres and matrix plastic. Moreover, the number of manufacturing stages is reduced and the manufacture is rapid. In an integrated structure the fastening element is attached to the wing rib without a discontinuation section, which is preferable regarding the strength of the structure. Some of the advantages of a composite structure in comparison with aluminium are, for example, a better stiffness and weight ratio and the fact that the composite properties can be controlled in many ways by selecting the reinforcing fibres and the matrix plastic appropriately and also by directing the reinforcing fibres.
In this application an aircraft refers to different airplanes, airships, satellites and possibly other equipment moving in the air.
Here, a wing refers, in addition to wings providing the lift of an aircraft, also to control surfaces used for controlling and managing aircrafts, such as elevators and rudders of airplanes, in the frame structures of which the invention in this application can be utilized.